"The first vehicle of the Chemical Weapons Investigation Team was deliberately shot at multiple times by unidentified snipers in the buffer zone area," a spokesman said.

No injuries were reported, but the lead car was damaged, causing investigators to return to a government checkpoint where they will obtain a new vehicle and return to the site.

"It has to be stressed again that all sides need to extend their cooperation so that the team can safely carry out their important work," the spokesman added.

Syrian state media claimed an unknown source had told them "armed terrorist groups opened fire on members of the UN team" as they were entering the al-Muadamiya area.

The UN inspection team entered Syria on Aug. 18 with the government's approval to visit three suspected chemical weapon attack sites. A new incident occurred on Aug. 21, and doctors and activists claimed an unidentified nerve agent had killed hundreds of innocent civilians. Investigators were then granted access to the site outside the capital city.

The experts were on their way there to take tissue, soil, blood and urine samples from victims when they were attacked. Still, even if they reach the area, the United States says evidence from the attack has likely deteriorated or been destroyed by heavy government shelling.

Assad has repeatedly dismissed the idea that his forces have used chemical weapons, while a senior Obama administration official recently said there was “very little doubt” the regime had used chemical weapons against civilians.

France, the UK, Turkey and Germany have all said they would support some sort of international response to the alleged chemical attacks, even if the UN Security Council remains split along its usual political lines, with Russia - Assad's stalwart ally - attempting to block military intervention.

On Monday, Chancellor Angela Merkel's spokesman Steffen Seibert said Germany would back a military response in Syria if it were somehow proven that Assad's forces had used chemical weapons.

"Germany would be among those who consider consequences to be appropriate," said Foreign Minister Guido Westerwelle in a statement on Monday.

The US and its allies believe Syria has stockpiles of sarin and mustard gas, though the regime has never admitted to possessing chemical weapons. Syria is one of the few nations that has not agreed to the landmark 1997 agreement to ban chemical weapons.